With rapid development of Reconfigurable Optical Add-Drop Multiplexer (ROADM) technologies, a colorless, directionless, and contentionless (CDC) ROADM is a development direction of a future ROADM architecture. Colorless means that any port can be used for outputting any wavelength, directionless means that any wavelength can be scheduled to any direction, and contentionless means that there is no wavelength conflict when a same wavelength needs to be locally added and dropped simultaneously in multiple directions.
As shown in FIG. 1, an ROADM architecture includes a line-side wavelength switching module and a client-side wavelength switching module. The line-side wavelength switching module is connected to the client-side wavelength switching module using an optical fiber. The line-side wavelength switching module may include multiple WSSs and splitters (SPs). One WSS and one SP constitute a wavelength switching sub-module in one direction. FIG. 1 shows wavelength switching sub-modules in three directions, including an east dimension, a west dimension, and a north dimension. The client-side wavelength switching module includes an add module and a drop module. The add module includes multiple transmitters (designated as TX) and one WSS, and the drop module includes multiple receivers (designated as RX) and one WSS. The east dimension is used as an example. For a Wavelength Division Multiplex (WDM) optical signal input from the east dimension, the optical signal is first broadcast to other several dimensions and the client-side drop module using an SP. For a wavelength that needs to be locally downloaded from the client side, the client-side drop module selects and receives the wavelength. For a wavelength that needs to be transferred from a WSS in the east dimension to a WSS in the west dimension, the WSS in the west dimension selects the wavelength and transfers the wavelength, and blocks wavelengths that are from other dimensions.
WSSs in other approaches have beam multiplexing and beam demultiplexing functions. FIG. 2A is a schematic diagram of a top view of an optical path structure of an N×M WSS in the other approaches. FIG. 2B is a schematic diagram of a side view of an optical path structure of an N×M WSS in the other approaches. As shown in FIG. 2A and FIG. 2B, a WDM signal is input from an input port 201 (i.e., an input optical fiber), is collimated by a collimator array 202, and is demultiplexed into K sub-wavelength signals by a first-stage grating 203. The K sub-wavelength signals are incident to a first-stage optical switching array 206 after passing through a cylindrical lens array 204 and a lens 205. The first-stage optical switching array 206 has N rows, and there are K optical switch units in each row. Each optical switch unit deflects one sub-wavelength signal such that the sub-wavelength signal is incident to a corresponding optical switch unit in a second-stage optical switching array 207. The second-stage optical switching array 207 has M rows, and there are K optical switch units in each row. Each optical switch unit corresponds to one sub-wavelength signal. The optical switch unit corrects an angle of the sub-wavelength signal such that the sub-wavelength signal is parallel to a direction of an optical axis (Z) in a YZ plane. All sub-wavelength signals are incident to a second-stage grating 210 after passing through a lens 208 and a cylindrical lens array 209, output to a collimator array 211 after being multiplexed by the second-stage grating 210, and finally output from an output port 212 (i.e., an output optical fiber). Actually, the first-stage optical switching array 206 and the second-stage optical switching array 207 perform optical switching only on a YX plane, and each optical switch unit implements a wavelength selection function by performing deflection in one dimension. The first-stage grating 203 and the first-stage optical switching array 206 implement a “beam demultiplexing” function, and switch the sub-wavelength signals from the same input port to different optical switch units in the second-stage optical switching array 207. The second-stage optical switching array 207 and the second-stage grating 210 implement a “beam multiplexing” function.
The second-stage optical switching array 207 requires M×K switch switching units. The K switch units occupy spatial positions in an X direction, and K is a relatively large integer. As a result, optical switching cannot be implemented in two dimensions. Therefore, output ports are restricted in one dimension and cannot be arranged in two dimensions, each output port corresponds to the K optical switch units, and a quantity of the output ports is restricted.